The invention is based on an injection valve as defined hereinafter. An injection valve is already known in which flow openings extend in an insert body such that the fuel streams emerging from them are aimed at the valve needle. As a result, the fuel must first be deflected toward the valve seat face, causing flow losses that reduce the energy available for fuel preparation.
An injection valve is also known in which to improve the sprayed fuel stream, swirl grooves are provided upstream of the valve seat, extending parallel to the longitudinal axis of the valve, which serve to make the fuel turbulent even before it flows through the valve seat. These swirl grooves impose a tangential force component upon the fuel emerging from the spray opening, causing the fuel to be ejected in a conical spray pattern. This inherently favorable effect can be only partly exploited in this known injection valve, however, because after emerging from the swirl grooves, which are machined into the circumference of the valve needle, the fuel flows into the vicinity of the undercut (which is required for manufacturing reasons), where it is slowed down severely. A further disadvantage of this known injection valve is that the metering of the fuel quantity injected per unit of time is determined, in such an injection valve, by the size of the flow cross section of the spray opening downstream of the valve seat with the valve opened. As a result, over relatively long operation the deposits that unavoidably form during use can reduce the cross section, hence leading to reduced flowthrough quantities. This phenomenon of "leaning down" is feared. It also arises with other embodiments of the metering zone, as long as such a zone is located downstream of the valve seat and hence is exposed to the atmosphere of the intake tube.
Another known injection valve, by comparison, offers the advantage that the quantity of fuel to be sprayed is metered upstream of the valve seat. To this end, metering bores are provided in the lower guide section of the valve needle, by way of which bores the fuel flows with a pressure drop. No provisions are apparent for generating any swirl in the fuel, however. Furthermore, the disposition of the metering bores on the valve needle is disadvantageous from a manufacturing standpoint because it also requires machining of the high-quality valve needle material. For atomizing the fuel, there is a needle pintle located inside the spray opening.